Antioxidant Properties of the Ethyl Acetate Fraction of Intsia Palembanica (Merbau, Fabaceae)

Intsia palembanica (Fabaceae) is a tropical heartwood indigenous to Malaysia and countries of similar climates. The tree is commercially used for its timber. The aim of this study was to examine the antioxidant capacity of I. palembanica, reputedly rich in polyphenols, with a view to exploiting its sawdust as a source of antioxidants for the pharmaceutical and/or nutraceutical industries. The ethyl acetate fraction of I. palembanica was assessed for total phenolics and for antioxidant activity by several methods, viz, DPPH radical scavenging assay, ferrous chelating ability and inhibition of xanthine oxidase in purine metabolism. The results showed the ethyl acetate extract of I. palembanica to be a potent antioxidant, in vitro. Total phenolics in the extract was 668.2 ± 58.2 μg catechin equivalents/g. Median effective concentrations (EC₅₀) for DPPH scavenging were 7.9±0.01 μg/mL and 4.5±0.02 μg/mL for the extract and standard antioxidant, trolox, respectively. EC₅₀ for Fe2+ chelation was 19.95±2.37 mg/mL and 0.032±0.002 mg/mL for the extract and its comparator, EDTA. I. palembanica was very potent in inhibiting the production of uric acid with IC₅₀ value of 6.3±2.5 μg/mL comparable to allopurinol which was 4.0±1.0 μg/mL. Median inhibitory concentrations (IC₅₀) for inhibition of tertbutylhydroperoxide was 1.26 μg/mL, in comparison to the standard antioxidants, alpha-tocopherol acetate (IC₅₀ = 1.58 μg/mL) and trolox (IC50 = 3.98 μg/mL). In summary, the ethyl acetate fraction of Intsia palembanica showed very potent antioxidant activity via various mechanisms. This holds promise for its use as a phytoantioxidant.

Keywords: Intsia palembanica; Antioxidant; Microsomal lipid peroxidation; DPPH; Fe2+; Xanthine oxidase